1. Field of the Invention
The present invention relates to a power semiconductor device and can be applied to, e.g., a thyristor, an IGBT or the like.
2. Description of the Background Art
In a general-type structure of a reverse blocking thyristor, conventionally, in a lower surface of a semiconductor substrate of a first conductivity type, an anode electrode region of a second conductivity type is formed.
Both side surface portions of the semiconductor substrate have a mesa structure. A lower side surface end of the semiconductor substrate, however, has a portion which is substantially vertical to a lower surface (hereinafter, referred to as “vertical portion”) in order to prevent a crack in a manufacturing process or the like. In other words, in a predetermined range from the lower surface of the semiconductor substrate, the side surface portion of the semiconductor substrate is the vertical portion and the vertical portion is connected to a mesa portion thereabove.
In a cross section, the anode electrode region is formed entirely in the lower surface of the semiconductor substrate. Further, the impurity diffusion length (height) of the anode electrode region reaches the mesa portion formed above the vertical portion in order to relieve an electric field at the mesa portion of the semiconductor substrate in applying a reverse voltage.
A technique relating to the above conventional structure is disclosed in Japanese Patent Application Laid Open Gazette No. 10-190012 (Patent Document 1).
As discussed above, a thyristor needs a vertical portion of about 40 to 50 μm in the lower side surface end of the semiconductor substrate, in order to prevent a crack. Further, in order to relieve an electric field at the mesa portion on the side surface portion of the semiconductor substrate and provide the thyristor with a reverse voltage breakdown voltage in applying a reverse voltage, it is necessary for the impurity diffusion length (height) of the anode electrode region to reach the mesa portion above the vertical portion.
For the above reason, in the conventional structure, the impurity diffusion length (height) of the anode electrode region is very long (high) (at least, 50 μm or more).
Thus, as the impurity diffusion length (height) of the anode electrode region becomes longer (higher), the magnitude of a reverse current at the turn-off disadvantageously increases (in other words, a recovery loss increases). If a predetermined system carries the thyristor with large recovery loss, the efficiency of the whole system becomes low.